Unraveling the excitation mechanisms of highly oblique lower-band chorus waves

Wen Li; D Mourenas; A. V Artemyev; J Bortnik; R. M Thorne; C. A Kletzing; W. S Kurth; G. B Hospodarsky; Geoffrey D Reeves; Herbert O Funsten; H. E Spence

doi:10.1002/2016GL070386

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Unraveling the excitation mechanisms of highly oblique lower-band chorus waves

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Unraveling the excitation mechanisms of highly oblique lower-band chorus waves

Wen Li, D Mourenas, A. V Artemyev, J Bortnik, R. M Thorne, C. A Kletzing, W. S Kurth, G. B Hospodarsky, Geoffrey D Reeves, Herbert O Funsten, …

Geophysical research letters, Vol.43(17), pp.8867-8875

08/17/2016

DOI: 10.1002/2016GL070386

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Abstract

Excitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth's magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100–500 eV in the parallel velocity distribution. The second mechanism corresponds to Landau resonance with a 100–500 eV beam. In both cases, a small low-energy beam-like component is necessary for suppressing an otherwise dominating Landau damping. In conclusion, our new findings suggest that small variations in the electron distribution could have important impacts on energetic electron dynamics.

Beam instability

GEOSCIENCES

Heliospheric and Magnetospheric Physics

Lower band chorus

oblique chorus excitation

Temperature anisotropy

Details

Title: Subtitle: Unraveling the excitation mechanisms of highly oblique lower-band chorus waves
Creators: Wen Li - Boston University
D Mourenas - Atomic Energy (Canada)
A. V Artemyev - University of California, Los Angeles
J Bortnik - University of California, Los Angeles
R. M Thorne - University of California, Los Angeles
C. A Kletzing - University of Iowa
W. S Kurth - University of Iowa
G. B Hospodarsky - University of Iowa
Geoffrey D Reeves - Los Alamos National Laboratory
Herbert O Funsten - Los Alamos National Laboratory
H. E Spence - University of New Hampshire
Resource Type: Journal article
Publication Details: Geophysical research letters, Vol.43(17), pp.8867-8875
DOI: 10.1002/2016GL070386
ISSN: 0094-8276
eISSN: 1944-8007
Publisher: American Geophysical Union
Grant note: DOI: 10.13039/100000104, name: National Aeronautics and Space Administration, award: NNX15AF61G, NNX14AI18G, NNX13AI61G; DOI: 10.13039/100000181, name: Air Force Office of Scientific Research, award: FA9550‐15‐1‐0158
Language: English
Date published: 08/17/2016
Academic Unit: Physics and Astronomy
Record Identifier: 9984199675002771

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